Jet pumping system for a nuclear reactor



Sept. 3, 1968 c. L. HOWARD JET PUMPING SYSTEM FOR A NUCLEAR REACTOR Original Filed July 30, 196

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JET PUMPING SYSTEM FOR A NUCLEAR REACTOR Original Filed July 30, 1965 4 Sheets-Sheet E Sept 3, 1968 C. I.. HQWARD 3,400,047

JET PUMPING SYSTEM FOR A NUCLEAR REACTOR Original Filed July 30, 1965 4 Sheets-Sheet Sept. 3. 1968 C. L. HQWARD 3,400,047

JET PUMPING SYSTEM FOR A NUCLEAR REACTOR Original Filed July 30, 1965 4 Sheets-Sheet 4 /V? /20/4/ /l/f// F//i/ fam/4m) INVENTOR (5V/1&5? L HUA/AQ@ United States Patent' 3,400,047 v v JET PUMPING SYSTEM FOR A NUCLEAR REACTOR t Charles L. Howard, San `lose, Calif., assignor to vGeneral Electric Company, New York, N.Y., a corporation of New York Original application July 30, 1965, Ser. No. 476,108, now Patent No. 3,373,688, dated Mar. 19, 1968. Divided and this application Feb. 21, 1967, Ser. No.630,166

8 Claims. (Cl. 176-56) ABSTRACT OF THE DISCLOSURE This describes an improved jet pump capable of controllable reverse flow for controlling the coolant ow in a reactor vessel through the ynuclear reactor core. The pump body is provided with at least one auxiliary driving fluid jet adapted to permit a controllable flow through the pump in the reverse direction from normal llow.

This application is a divisional of patent application Ser. No. 476,108, entitled, Pumps, tiled July 30, 1965, by Charles L. Howard, now Patent 3,373,688, granted Mar. 19, 1968.

This invention relates to jet pumps and improved controls for them.

This invention can be used in a Wide variety of applications, but it is ideally suited for controlling jet pumps used to circulate uid coolant in boiling nuclear reactors, and is particularly described for that use. A boiling nuclear reactor usually includes a reactor pressure vessel with a nuclear reactor core located inside it. A lluid coolant surrounds the core, and a control system is mounted to be moved into and out of 'the core to control the rate of nuclear reaction, which in turn controls the rate of heat generation.

In a heterogeneous reactor, which is the type described here, the fluid coolant is liquid, and at least a portion of it is converted into vapor within the reactor core. -The coolant, in addition to absorbing heat from the core, also acts as a moderator because it slows down neutrons produced by the nuclear reaction and regulates the rate of fission within the core;

A typical coolant may be light water, heavy water, or an organic liquid such as diphenyl, or any other fluid having suitable physical characteristics as both a moderator and a coolant. In a typical boiling nuclear reactor, vapor generated in the reactor core is caused to flow from the reactor vessel to a prime mover, such as a steam turbine. Vapor passing through the turbine is condensed to liquid and returned to the pressure vessel.

For a more complete discussion of boiling reactors, see `Boiling Water Reactors by Kraemer, published by Addison-Wesley Publishing Company.

In the reactor core of a boiling reactor, the moderating coolant is present in both a liquid and a vapor phase. The moderator-to-fuel ratio in a reactor determines nuclear reactivity, and the tolerable range of the ratio is set by the reactor design. The boiling, moderating coolant has a number of vapor -bubbles dispersed in it. The ratio of the vapor bubbles to the liquid-state coolant is the void fraction of the coolant. The moderator-to-fuel ratio is decreased as boiling increases because the vapor bubbles have a density much less than the liquid state of the moderator coolant.

In a reactor design of this type, the magnitude of the coolant flow is important with respect to reactor power level variation as well as adequate fuel cooling. For example, a controlled decrease in ow rate increases the number of voids, decreases the neutron moderator content, and thus decreases the reactor power level. On the Frice other hand, a controlled increase in ow rate decreases the number of voids, increases the neutron moderator content, and thus increasesv the reactor power level. vvThe reactor can be designed to accomplish these power and ilow variations while still providing adequate reactor lfuel cooling. v`

VJet pumps have been mounted within the pressure vessel tol provide controlled circulation of moderator coolant through the core. The jet pumps do a goodjob because they are relatively inexpensive, and have no moving parts. y

A conventional jet pump includes a body with three distinct regions, namely, an inlet or suction section, a throat or a mixing chamber vof substantially uniform cross-sectional area throughout its length, and a diffuser which increases in cross-sectional area in the direction of flow. A nozzle is positioned in the inlet section to convert a high-pressure stream of driving fluid into a highvelocity, low-pressure jet'of driving Huid which ilows coaxially through the inlet section and into the mixing chamber. The high-velocity jet is at a much lower pressure than iluid surrounding the nozzle in the Vicinity of the inlet section so driven lluid is sucked into the pump inlet by the jet. A converging housing on the inlet section and surrounding the nozzle directs the driven fluid or suction flow into the mixing chamber. Within the mixing chamber, the high-velocity jet of driving uid gradually widens as an entrainment-mixing process takes place with the driven lluid or suction stream. The mixing transfers momentum from the jet driving stream to the driven suction stream, so pressure in the combined stream rises. In theory, the mixing chamber ends after a uniform velocity profile is achieved, and this usually occurs shortly after the widening driving jet stream touches the mixing chamber walls. From the relatively small cross-sectional area mixing chamber, the merged driving and driven iiuids flow into the diffuser of increasing cross section in the direction of flow, further increasing pump discharge pressure as the velocity of the merged fluids is reduced to extract the optimum amount of energy from the stream.

One of the advantages of jet pumps in boiling nuclear reactors is that the pumps have excellent natural circulation characteristics. Even when the driving fluid is turned oli at the nozzle, there is still a substantial amount of flow through the jet pumps because of convection currents generated in the pressure vessel due to the heat in the core. However, this flow characteristic limits the control that can be exercised with conventional jet pumps installed in boiling nuclear reactors.

-Prior to this invention, conventional jet pumps could be controlled only between about 40% to 100% of total flow. In other words, even with the jet pumps turned ol, their good natural circulation characteristics still permit liquid to flow through the pumps at a rate equal to about 40% of the full capacity of the pump. This invention provides an auxiliary reverse-flow nozzle for a jet pump so that the range of its control is increased from 100% forward flow to 100% backward flow.

When using jet pumps in a nuclear reactor, or other applications, it is desirable to be able to control the flow rate of the jet pumps smoothly through a wide range. By sequential llow reversal of several jet pumps out of a total of perhaps twenty in a reactor, the total Huid-flow through the reactor core can be changed to any value from the maximum down to zero.

The improved jet pump of this invention includes an elongated, hollow pump body having an inlet and an outlet. The pump body includes a mixing chamber and a difadjacent the pump inlet to direct a jet of driving fluid into the mixing chamber and toward the pump outlet. A reverse-flow nozzle is mounted adjacent the pump outlet to direct a jet of fluid into the pump `body toward the pump inlet.

In the preferred form of the invention, a source of fluid pressure is connected to both the forward-flow and reverse-flow nozzles in the pump, and control means are provided for varying the amount of fluid delivered to the nozzles. Preferably, the control means is a uid switch which is energized or de-energized by the application or removal of control uid pressure to the switch.

When one or more of the pumps of this invention are used in a jet pumping system for a pressure vessel, such as a nuclear reactor including a reactor including a reactor core, the pumps are mounted inside the pressure vessel to have their inlets connected to a core outlet and their outlets connected to a core inlet. Preferably, the fluid switch is located outside the pressure vessel to facilitate control and maintenance of the uid through the jet pumps within the vessel.

Preferably, the reverse-flowjets are controlled independently of each other so that the pumps can be actuated sequentially to flow in the reverse direction and provide a wide range of flow variation through the reactor core in the pressure vessel.

For maximum safety, the pumps are arranged to failsafe, i.e., prevent overheating or too rapid a reactivity increase by using a plurality of jet pumps, some of which are equipped with reverse-flow jets and others of which are not. A portion of those pumps equipped with reverseflow jets flow in a forward direction when their respective uid switches are energized, and the others ow in a forward direction when their switches are de-energized. The remaining jet pumps, which have no reverse-flow nozzles, flow in a forward direction independently of the condition of any of the fluid switches. In this way, even though control uid pressure is lost to all fiuid switches, an intermediate fluid ow rate is automatically established through the core to provide a safe operating condition.

These and other aspects of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a schematic elevation of jet pumps with and without reverse-flow nozzles mounted in a boiling nuclear reactor in accordance with this invention;

FIG. 2 is an enlarged schematic drawing showing how a fluid switch is used to control the flow of driving fluid to a jet pump which automatically pumps in a reverse direction if control pressure for the uid switch fails;

FIG. 3 is an enlarged schematic drawing showing how a fluid switch is used to control the driving fluid of a jet pump which automatically operates in the forward direction if control fluid to the fluid switch fails; and

FIG. 4 is an enlarged schematic drawing showing a plurality of reverse-flow nozzles mounted around the periphery of the mixing chamber for reversing fluid-flow through the pump.

Referring to FIG. l, a cylindrical reactor core is coaxially disposed within a cylindrical pressure vessel 11 closed at its top and bottom. A plurality of jet pumps 12, 13, and 14 are mounted in an annular downcomer space 15 formed between the reactor core and the wall of the pressure vessel.

A pool of water 16 is maintained at an operating level 17 above the height of the upper end of the reactor core. A separate forward-flow nozzle 18 is mounted adjacent the inlet 19 of each jet pump to direct a jet of high-velocity liquid down through the pump body, thus sucking driven fluid through the pump with it. The mixed driving and driven fluids are forced into the bottom of the reactor core as indicated by arrows 20 and fiow up through the reactor core where at least part of the water is converted to steam, which flows from the pressure vessel through a steam line 21 into a turbine 22. Steam passing through the turbine is condensed in a condenser 23 and returned as feedwater through a line 24 to a rst pump 2S having its inlet connected by a line 26 to the inlet of a driving pump 28 which is connected to a high pressure supply line 30 and a plurality of control systems 32 which are each connected to a respective nozzle 18 by a driving fluid line 34. A separate fiuid control line 31 is connected to each control system 32 for controlling the flow of fluid as described in detail below.

A separate reverse-flow line 36 is connected at one end to each control system 32 and is sealed through the wall of the pressure vessel and terminates in a respective reverse-flow nozzle mounted downstream of the forwardow nozzle serving the pump.

The control system and jet pumps are described in more detail below with respect to FIG. 2. Additional driving fiuid is taken as required from the pool of water through line 38 connected to the suction side ofpump 28. A valve 39 in line 38 controls the flow of fluid through the line.

In automatic control systems, the speed of pump 28 is controlled by a motor 40 which is supplied power from a variable-frequency generator 42. The generator is driven by a variable fluid coupler 44, which in turn is driven by a prime motor 46 connected to it. A control 48 on the variable fluid coupler determines the amount of power delivered by the prime motor 46 and the rate at which the variable-frequency generator is turned. This in turn controls the speed of motor 4t) and pump 28. This rather elaborate and expensive system has been required in the past to control the flow of fluid through the jet pumps, but in many installations can be eliminated by the use of reverse-flow nozzles in accordance with this invention.

At least one of the jet pumps (pumps 13 shown in FIG. 1) is mounted in the annular space 15 in the pressure vessel without a reverse-How nozzle. Pump 13 receives driving Huid through line 30 and can pump only in the forward direction, unless turned off by operation of a valve 47 in line 30. Although only three jet pumps are shown in FIG. l, any desired number can be used. For example, twenty pumps may be employed. Twelve of the pumps have no fluid switches or reverse-flow jets. The remaining eight have flow switches and reverse-flow jets connected to operate as described in detail below.

Referring to FIG. 2, jet pump 12 includes a frustoconical inlet section 50 connected at its smaller end to the upstream end of an elongated, cylindrical throat or mixing chamber 52. The wider end of the inlet section opens toward the forward-flow nozzle 18, which is collinear with the longitudinal axis of the mixing chamber.

The opposite or downstream end of the Imixing chamber is connected to the smaller end of frusto-conical diffuser 54 which discharges at its lower end into the underside or inlet of the reactor core shown in FIG. l.

The control device 32 can be any suitable unit which can divert all or part of the driving fluid from the nozzle 18 to a reverse-how nozzle 55 mounted in the diffuser collinear with the mixing chamber longitudinal axis to direct a jet of fluid from the pump outlet to the pump inlet. A fluid switch 56 makes an ideal control system for switching driving fluid between the forward-ow nozzle and the reverse-flow nozzle.

Fluid switches are descr-ibed in detail in Scientific American, December 1964, pages -88.

A prime advantage of this invention is that the control system is outside the pressure vessel, and no moving parts are required within the vessel to achieve the increased recirculation flow range. In some installations, the irnproved control eliminates the necessity of the variablepower generator 42, variable uid coupler 44, and prime motor 46. In these cases, the feedwater pump 28 can always be operated at rated speed, and the energy addition to the recirculation flow is controlled by the ow spoiler system. Of course, the spoiler technique of this rinvention can also be used to control fluid-fiow through jet pumps even when feedwater is not introduced through the jet pump nozzles.

Driving fluid from high-pressure supply line 30 enters an inlet 57 of the fluid switch, and normally would flow straight through the control device and out a first outlet 58 connected to the reverse-flow nozzle 55. However, a small stream of control liquid under pressure is injected through control line 31 just upstream of a pointed stream splitter 60 formed where first outlet 58 and a second outlet 61 leave the flu-id switch. Second outlet 61 is connected to the forward-flow nozzle 18. The control stream is directed against the right (as viewed in FIG. 2) side of the main flow of driving fluid, and diverts it to the left so that all of the driving fluid flows out the second outlet 61. In this condition, the pump is full-on because all of the driving fluid flows out forward-flow nozzle 18 and into the mixing chamber of the jet pump. To reverse the pumping direction, the control stream is turned oil so the driving fluid now flows straight through the switch and out the first outlet 58 to the reverse-flow nozzle 55 to drive fluid through the pump in the opposite direction. By adjusting the strength or pressure of the control stream, the amount of fluid flowing through the reverse-flow nozzle is varied from zero to 100% of the volume of the fluid passing through the fluid switch. Thus, not only can the pump be turned off, but it can be made to pump in the reverse direction, completely overcoming the natural circulation which would flow through the pump if the reverseflow nozzle were absent. Moreover, if control fluid pressure should fail, pump 12 will automatically pump in the reverse direction.

Pump 14 shown in FIG. 3 is identical with that of the pump shown in FIG. 2 except the fluid switch 56 is connected to pump 14 so that if the fluid control pressure fails, pump 14 will automatically pump Iin a forward direction.

In the pump shown in FIG. 3, driving fluid enters the fluid switch inlet 57 from high-pressure supply line 30 and passes straight through the switch and out first outlet 58 connected to the forward-flow nozzle 18. Ordinarily, no control fluid pressure is appl-ied through line 31, so that the pump operates in the forward direction. To reverse the pump, a stream of control liquid is injected under pressure through control signal line 31 just upstream of the pointed stream splitter on the left side of the driving fluid to shift the driving fluid to the right and out the second outlet 61, which is connected to the reverse-flow nozzle 55. Under this condition, pump 14 is operated in the reverse direction. By adjusting the strength and pressure of the control stream, the amount of fluid flowing through the reverse-flow nozzle is adjusted from zero to 100% of the fluid volume passing through the fluid switch.

Control of the total fluid-flow through the reactor core is achieved by independent and sequential control of the individual jet pumps. For example, starting from maximum forward flow for all jet pumps, the sequence for flow reduction is as follows, assuming a total of twenty jet pumps:

(1) Reduce gradually the forward flow in jet pump No. l until its flow is maximum in the reverse direction. The total core flow is (as a first approximation) reduced to 18/20 of its original value.

(2) Reduce gradually the flow in a second jet pump (preferably located on the opposite side of the reactor from the first) until its flow is a maximum in the reverse direction. The core flow is now roughly 16/20, or less, of the original value.

(3) From the foregoing, it is seen that the core flow can be reduced to zero by reversing the flow in about one-half of the jet pumps. It is, therefore, necessary to provide flow-reversing jets on less than one-half of the jet pumps. For example, the reversing jets are provided on every second or third jet pump.

An important safety aspect of this invention is the CFI ability to provide for the inadvertent loss of flow to the control lines of the fluid switches. If such loss occurs, it is desired that the system be fail-safe.

The meaning of fail-safe in this system is not immediately obvious. The required considerations include the following:

(l) When the reactor is at a low core flow condition, it `is important that failure of a fluid switch control line not result in a sudden increase of reactor flow rate. If such a flow increase were too rapid (relative to fuel time constant), the decrease in core voids could result in too rapid a reactivity increase and a potentially serious accident. With this consideration in mind, flow rate through the core must not increase too fast in the event of failure of control lines to the fluid switches.

(2) When the reactor is operated with higher fluid-flow rates through the core, it is important that failure of the fluid switch control lines does not result in too rapid a decrease in core flow, so that the critical heat flux limit for the fuel is reached during the flow transient. In order to be fail-safe in this event, adequate flow should continue through the core when no control flow is applied to the fluid switches.

(3) The requirements of both (l) and (2) immediately above are satisfactorily met by using a combination system which solves the advantages of both items (1) and (2) above. For example, a reactor having twenty jet pumps is arranged to have fluid switch -controls as follows.

No. of jet pumps: Type of fluid switch control Twelve No fluid switches or reverse-flow jets. Four Fluid switch directs flow to forward-flow jet if control flow is lost (FIG. 3). Four Fluid switch directs flow to reverse-flow jet if control flow is lost (FIG. 2).

With this arrangement, if the control flow of all the fluid switches is lost, the reactor flow comes to an equilibrium condition that is safe. The sixteen jet pumps supplying for- Ward-flow and four supplying reverse-flow give a total reactor core flow of approximately 12/20 or 60% of the maximum flow rate. Choice of this equilibrium flow rate results in a relatively small transient when starting from either high flow or low flow conditions. The exact number of jet pumps with each control arrangement is adjusted to account for design requirements for a particular application and for the forward-to-reverse flow capacity ratio of particular jet pump designs. It is also necessary to consider the sequencing for normal flow reversal of the jet pumps of the two control arrangements so that the flow transients are acceptable regardless of the reactor flow at the start of the transient.

The advantages of pumping systems made in accord- -ance with this invention include the following:

(l) It provides a wide range of carefully controlled flow variation through a reactor core.

(2) It maintains flow stability or stiffness at low flow rates.

(3) The control devices are simple, reliable, and have a long life. They are particularly well suited for nuclear reactor installation because they do not use any moving parts.

(4) The system reduces flow through jet pumps well below the natural circulation levels, and in fact can reverse the direction of flow through the pumps.

FIG. 4 shows an alternate embodiment of a pump which is similar to that shown in FIG. 2, except that a plurality of reversing nozzles are disposed in an annular configuration inside the discharge end of the mixing chamber and coaxially in the mixing chamber. Reversing fluid is supplied to the reverse-flow nozzles from the first outlet 58 of the fluid switch 56. The outlet 58 is connected to a manifold 72 which supplies liquid to all of the reverseflow nozzles. The remainder of the pump is identical with that shown in FIG. 2, and a detailed description of the elements is not repeated here for brevity.

I claim:

. 1. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and outlet in the vessel, a jet pumping system comprising: an elongated, hollow pump body having an inlet and an outlet in the vessel, the pump outlet being connected to the core inlet, and the pump inlet being connected to the core outlet, the pump body including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the pump inlet, and the diffuser opening at one end to the pump outlet, a forwardflow nozzle mounted adjacent the pump inlet to direct a jet into the mixing chamber and toward the pump outlet, and a reverse-flow nozzle mounted adjacent the pump outlet to direct a jet into the pump body toward the pump inlet.

2. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: an elongated, hollow pump having an inlet and an outlet in the vessel, the pump outlet being connected to the core inlet, and the pump inlet being connected to the core outlet, the pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the pump inlet, and the diffuser opening at one end to the pump outlet, a forward-flow nozzle mounted adjacent the pump inlet to direct a jet into the mixing chamber and toward the pump outlet, a reverseflow nozzle mounted adjacent the pump outlet to direct a jet into the pump toward the pump inlet, a source of fluid pressure, a fluid switch having an inlet and two outlets, means connecting the fluid switch outlets to one of the nozzles, means connecting the other fluid switch outlet to the other nozzle, and control means for the fluid switch to regulate the amount of fluid delivered from the source to the nozzles.

3. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: an elongatetd, hollow pump having an inlet and an outlet in the vessel, the pump outlet being connected to the core inlet, and the -pump inlet being connected to the core outlet, the body including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the pump inlet, and the diffuser opening vat one end to the pump outlet, a forward-flow nozzle mounted adjacent the pump inlet to direct a jet into the mixing chamber and toward the pump outlet, a reverse-flow nozzle mounted adjacent the pump outlet to direct a jet into the pump toward the pump inlet, a source of fluid pressure, a fluid switch disposed outside the pressure vessel and having an inlet and two outlets, means connecting the lluid switch inlet to the source of fluid pressure, means `connecting one of the fluid switch outlets to one of the nozzles, means connecting the other fluid switch outlet to the other nozzle, and control means outside the pressure vessel for the lluid switch to regulate the amount of fluid delivered from the source to the nozzles.

4. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: a, pair of elongated, hollow pumps, each having an inlet and an outlet, in the vessel, each pump outlet being connected to the core inlet, and each -pump inlet being connected to the core outlet, each pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to a respective pump inlet, and the diffuser opening at one end to a respective pump outlet, a separate forward-flow nozzle mounted adjacent each pump inlet to direct a jet into the mixing chamber and toward the respective pump outlet, a separate reverse-flow nozzle mounted adjacent each pump out-let to direct a jet into the pump toward the respective pump inlet, a source of lluid pressure, a pair of iluid switches, each having an inlet and two outlets, means connecting each fluid switch inlet to the source, means connecting one of the outlets of one of the fluid switches to one of the nozzles of one of the pumps, means connecting the other outlet of the said one fluid switch to the other nozzle of the said one pump, means connecting one of the outlets of the other lluid switch to one of the nozzles of the other pump, means connecting the other outlet of the said other fluid switch to the other nozzle of the said other pump, and separate control means -for each of the fluid switches to regulate independently the amount of fluid delivered from the source to the nozzles.

5. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: first and second elongated, hollow pumps, each having an inlet and an outlet, in the vessel, the pump outlets being connected to the core inlet, and the pump inlets being connected to the core outlet, each pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the respective pump inlet, and the diffuser opening at one end to the respective pump outlet, a separate forwardflow nozzle mounted adjacent each -pump inlet to direct a jet into the mixing chamber and toward the respective pump outlet, a separate reverse-flow nozzle mounted adjacent each pump outlet to direct a jet into the pump toward the respective pump inlet, a source of fluid pressure, first and second fluid switches, each switch having an inlet and two outlets, means connecting each fluid switch inlet to the source, means connecting one of each of the fluid switch outlets to a respective one of the forward-flow nozzles, means connecting each of the other fluid switch outlets to a, respective reverse-flow nozzle, and separate control means `for energizing and de-energizing each fluid switch to regulate independently the amount of fluid delivered from the source to the nozzles, one of the fluid switches being constructed and arranged to direct at least a majority of the fluid flowing t-hrough it to the reverse-flow nozzle of a pump when de-energized.

6. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: first and second elongated, hollow pumps, each having an inlet and an outlet, in the vessel, the pump outlets being connected to the core inlet, and the pump inlets being connected to the core outlet, each pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the respective pump inlet, and the diffuser opening at one end to the respective pump outlet, a separate forward-flow nozzle mounted adjacent each pump inlet to direct a jet into the mixing chamber and toward the respective pump outlet, a separate reverse-flow nozzle mounted adjacent each pump out-let to direct a jet into the pump toward the respective pump inlet, a source of fluid pressure, first and second fluid switches, each switch having an inlet and two outlets, means connecting each fluid switch inlet to the source, means connecting one of each of the fluid switch outlets to a respective one of the forward-flow nozzles, means connecting each of the other fluid switch outlets to a respective reverse-flow nozzle, and separate control means for energizing and deenergizing each fluid switch to regulate independently the amount of fluid delivered -from the source to the nozzles, one of the fluid switches being constructed and arranged to direct at least a majority of the fluid flowing through it to the forward-flow nozzle of a pump when de-energized.

7. In a nuclear reactor having a pressure vessel adapted to hold a fluid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: first and second elongated, hollow pumps, each having an inlet and an outlet, in the vessel, the pump outlets being connected to the core inlet, and the pump inlets being connected to the core outlet, each pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the respective pump inlet, and the diffuser opening at one end to the respective pump outlet, a separate forward-flow nozzle mounted adjacent each pump inlet to direct a jet into the mixing chamber and toward the respective pump outlet, a separate reverse-ow nozzle mounted adjacent each pump outlet to direct a jet into the pump toward the respective pump inlet, a source of Huid pressure, rst and second uid switches, each switch having an inlet and two outlets, means connecting each iiuid switch inlet to the source, means connecting one of each lof the uid switch outlets to a respe-ctive one of the forward-How nozzles, means connecting each of the other fluid switch outlets to a respective reverse-flow nozzle, and separate control means for energizing and de-energizing each fluid switch to regulate independently the amount of uid delivered from the source to the nozzles, one of the iiuid switches being constructed and arranged to direct at least a majority of the flu-id owing through it to the reverse-flow nozzle of the first pump when de-energized, the other uid switch being constructed and arranged to direct at least a majority of the fluid flowing through it to the forward-flow nozzle of the second pump when de-energized.

8. In a nuclear reactor having a pressure vessel adapted to hold a uid, and including a nuclear reactor core having an inlet and an outlet in the vessel, a jet pumping system comprising: first and second elongated, hollow pumps, each having an inlet and an outlet, in the vessel, the pump outlets being connected to the core inlet, and the pump inlets being connected to the core outlet, each pump including a mixing chamber and diffuser connected in series, the mixing chamber opening at one end to the respective pump inlet, and the diffuser opening at one end to the respective .pump outlet, a separate forward-flow nozzle mounted adjacent each pump inlet to direct a jet into the mixing chamber and toward the respective pump outlet, a separate reverse-flow nozzle mounted adjacent each pump outlet to direct a jet into the pump toward the respective pump inlet, a source of uid pressure, first and second fluid switches, each switch having an in-let and two outlets, means connecting each uid switch inlet to the source, means connecting one of each of the fluid switch outlets to a respective one of the forward-W nozzles, means connecting each of the other fluid switch outlets to a respective reverse-flow nozzle, separate control means for energizing and de-energizing each u-id switch to regulate independently the amount of fluid delivered from the source to the nozzles, one of the fluid switches being constructed and arranged to direct at least a majority of the iluid flowing through it to the reverse-How nozzle of the rst pump when de-energized, the other fluid switchI bein-g constructed and arranged to direct at least a majority of fluid owing through it to the forward-flow nozzle of the second pump when deenergized, and at least one other jet pump in the vessel mounted to pump fluid t-hrough the core independently of the condition of any of the fluid switches.

References Cited UNITED STATES PATENTS 2,861,033 11/1958 Treshow 176--56 3,154,140 10/1964 Esselman et al. 176-61 3,202,584 8/1965 Bogaardt et al 176-61 3,274,065 9/196-6 Kiergulf et al 176-56 REUBEN EPSTEIN, Primary Examiner. 

